Process of treating steel.



CHARLES HENRY AU'e srUs mmbnmcx LocxHABr BOSS, or. BALNAGOWN CASTLE,

. COUNTY or ROSS, sco'rmxm.

rnocnss of mmense STEEL.

No Drawing.

Toallwlzomit may concern:

Be it known that I, CHARLES HENRY AUoUs'rUs, FREDERICK LOCKHART Ross, a

subject of the King of Great Britain, residing at Balnagown 'Castle, Rossshire, Scotland, have invented certain new and useful Improvements in Processes of Treating Steel; and I do hereby declare the following to be a full, clear and exact descrlption of the invention, such as will enable others skilled in the art to which 1t appert-ains to make and use the same.

This invention relates to a process of treating steels, especially steels having a greater or less percentage of manganese, and has for its object to impart to a wlde range of carbon steels desirable properties such as an increase of their elastic limits, the

maintaining of the elongation of 'said steels at higher percentages, while also the maintaining in said steels their property of being machined, all as will appear below.

With these and other ob ects in view the invention consists in the novel heat treatments of said steels and combinations of treatments more fully hereinafter disclosed and particularly pointed out in the claims.

It is a well known expedient to sub ect steels of various compositions'to various heat treatments and to thereby impart to said steels, more or less valuable qualities.

For example in the Journal of The F rank- Zz'n Institute, volume 167, pages 379-391, there is disclosed a treatment of a chromvanadium steelqhaving the following analysis and physical properties:

Analysis: CO 36%, Mn. 0.21%, Cr. 2.78%, V O 24%. I

Physical tests: elastic limit 65 tons, ult1-' mate breaking 72 tons, elongation on 2" reduction of area 56. Treatment: 1500 Faquenched in 011, re-

' heated to1150 F. allowed to cool.

Also, in the Proceedings of thelron (fi steellnstitute, Vol. I of 1909, page 357, there is disclosed a carbon steel having the following analysis and physical properties:

Analysis: C, 0.75%, M11, 0.92. a

Physical tests: elastic'limit 62.6 tons per sq. inch, ultimatestress 73.7 tons per sq. inch, elongation on 2 15%, reduction of area 37.2%.

Treatment: 1560 .F. quenched in water,

reheated at 1100 and-cooled in air.

The above disclosures are the nearest I Specification of Letters Patent.

' bath.

Patented Aug..2a, 1915.

Application filed July 27, 1914. Serial No. 853,551.

1.25% to 1.3%; P, 0.045% to 0.05%; S,

0.45% to 0.05%. This steel maybe produced by any of the well known processes such as the crucible, open-hearth, Bessemer or electric, and when subjected to my treatment its physical properties are profoundly modified. and improved as will presently appear.

' In carrying out my process I take a steel such as that just mentioned for example, and first heat the same in a non-oxidizing medium such as a bath of molten metal or a salt whose temperature is maintained at from say 1400 to 1440 F. so that the cold steel whether a bar, a forging, a casting or other shape when placed in the bath, is

, heated rapidly to the temperature of said The external heat may be supplied by any suitable means but it should be of suchintensity as to transmit heat to the material of the bath at the rate of say 150 to 160 British thermal units per minute for each pound of steel heated. For example, a bar of steel one and one fourth inches (11") in diameter and eighteen inches long (18") should have its temperature raised throughout from 60 F. to 1400 F. in say six minutes. I accomplish this by making the bath of liquid metal of such a.volume that its fall in temperature when the cold steel is introduced will not exceed say, 20 F. The maintaining ofthis substantially constant temperature of the bath is greatly facilitated by so controlling the supply of ex ternal heat as to cause the steel being treated to acquirethroughout the temperature of the bath within say six minutes after it is introduced. I accomplish this latter result by the aid of pyrometers and suitably regulating the temperature.

Second. As soon as the steel is heated throughout to between say 1400 F. and 1425 F. and within the time specified, it is immediately quenched in a solution the composition and temperature of which is preferably as follows: For a bar of the size of that above mentioned salammoniac 4 oz.,

liquid is so maintained that the temperature of this cooling medium is kept substantially constant or between say 100 F. and 120 F.

Third. The completed, the steel is next reheated in the same kind of bath and in the same manner, but this time to from say 1000 F. to 1050 F. In practice I have found it more convenient to provide separate baths and furnaces for the two heating operations, so that the baths may be heated concurrently. In this second heat treatment the rate of heating of the steel is somewhat less than in the first treatment, in that only 80 to 85 British thermal units of heat per pound of steel is imparted to the bar instead of 150 to 160 of such units. Further the bar is preferably brought to the temperature of the bath, or raised from say 60 F. to 1000 F. in say about 8 minutes instead of in the time required in the first treatment. Also, the volume of and flow of heat to the second bath are so controlled that the temperature of the bath does not fall more than say 25 'F. during this second heat treatment.

Fourth. The bar having been subjected to the second bath for say 8 minutes and brought to the temperature stated, it is then immediately quenched in oil the temperature of which may be maintained at say 100 F. or it may be cooled in air, according to the degree of hardness required. The change of properties experienced by a rolled steel bar of the above analysis upon being subjected to my process may be understood from the following comparison of its properties before and after treatment:

- Elonga- Elon a- Reduci g g tion tion 0 'tion of m on 2.8' on 2". area.

Untreated 28 to 35 tons 40 to 48 25/30 28/35 50 to 60 Treated. 60to70tons to85tons 17 to 12% 23 to 17% 49 to 40 p e r s q p e r s q inch. inch. I

The steel thus treated is found to be neither oxidized toan appreciable extent, nor is its property of'machinability removed.

It will now be seen that by subjecting steel to my process the following results are attainedF- (a). The elastic limit, or point at which permanent deformation begins to take place in the steel when subjected to stress, is increased at least 100%. As is well known it .is more preferable to reckon from this point than from the place.

(b). The elongation of the steel, or the measure of toughness of the material under stress and strain, is maintainedat a higher point at which rupture takes percentage than' is found in other carbon,

steels of the same elastic limit.

(0). The reduction of area, another function of the physical properties is in quenching operation beingkeeping with the rest, and shows that the properties conferred by my process are not confined to the increase in the value of one function to the detriment of another.

(d). Another important and commercially valuable property, conferred 'by my process is that the steel treated by the afore= said process having a yield. or elastic limit of from 60 to 70 tons per square inch can be machined without difiiculty. I need not elaborate on this point, for it is recognized as one of the utmost importance from a commercial point of view.

(6). The steel being heated in a non-oxidizing medium such as a bath of liquid lead for example, its oxidation is prevented, hence finished articles can be treated by my process without any danger of surface deterioration.

(f). From an examination of the micro structure of the treated steel the sections show a complete uniformity of structure throughout. In fact a uniform distribution of the carbids of iron and manganese seems to be produced by my process. And without employing any of the many terms now used and misused for describing the different solutions of carbon in steel, it is safe to say after a very large number of experiments I have discovered, just that rate of heating a and cooling and those ranges of quenching temperatures, as well as that combination of treatments in relation to the steels in question, which go to produce a complete and uniform saturation of the contained carbon, iron and manganese, and I thereby attain the remarkable properties disclosed.

I am well aware that special properties of hardness and toughness produced in steel by this method-of treatment, are obtained within what are known as the critical temperature ranges of steels, and I therefore lay no claim to the discovery made several years ago, that all carbon and'alloy steels have definite critical temperatures (differing with their composition) in the region of which quenching produces the maximum hardness in the steel. As a matter of fact however very little is really known of the exact quenching temperatures that can be looked upon as reliable data for the hundred and one classes of steel. I however have established, not only on an experimental, but also on a commercial basis a process, which guarantees practical results exceeding any hitherto obtained from carbon steels so far as I am aware, and therefore I lay claim. to the discovery of those combinations of quenching temperatures, rates of heating above process has been disclosed in connection oply one analysis ofsteel, yet, my process has been actually applied to a wide range of carbon steels varying all the way from .251; carbon to over 1.00'j2 carbon content. It is therefore evident that those skilled in the art may widely vary the composition of the steel and also to some extent the above times and temperatures without departing from the spirit of my invention. Therefore. I do not wish to be limited to the above disclosure except as may be required by the claims.

What- I claim is:

1. The process of treating steel which consists in subjecting the same to a bath having a temperature substantially equal to the critical temperature of the steel while imparting to said bath in less than ten minutes more than 125 British thermal units per minute for each pound of steel being treated: immediately quenching the heated steel at a temperature below 150 F.; reheating said steel to substantially 1000 F.; and immediately quenching said reheated steel at a temperature below 120 F., substantially as described.

2. The process of treating steel which consists in subjecting the same to a non-oxidizing bath having a temperature of substantially 1400 F. while imparting to said bath in less than ten minutes more than 125 British thermal units-perminute for each pound of steel being treated; immediately quenching the heated steel at a temperature below 150 l.: reheating said steel to substantially 1000 F.: and immediately quenching said reheated steel at a temperature below 120 F.. substantially as described.

3. The process of treating steel which consists in subjecting the same to a bath of molten metal having a temperature of subtantially 1400 F. and imparting to said bath in less than ten minutes more than 125 British thermal units per minute for each ound of steel being treated; immediately quenching the heated steel at a temperature below 130 F.; reheating said steel to substantially 1000 F and immediately uenching said reheated steel at a temperature below 120 F., substantially as described.

4. The process of treating steel which consists in subjecting the same to a bath of molten metal having a temperature of substantially 1400 F. and imparting to said steel within a period of less than ten minutes more than 125 British thermal units of heat for each pound of steel: immediately quenching the heated steel. reheating said steel to a temperature of substantially 1000 F. and imparting thereto less than 125 Britl ll thermal units of heat for each pound of steel during a period of eight minutes; and immediately quenching said reheated steel, substantially as described.

5. The process of treating steel which consists in subjecting the same to a bath of molten metal having a temperature of substantially 1100 F. and imparting to said steel within a period of less than ten minutes more than 125 British thermal units of heat for each pound of steel: quenching the heated steel in a bath containing salammoniac. alum and common salt: reheating said steel to a temperature of substantially 1000*" F.. and imparting thereto less than 125 British thermal units of heat for each pound of steel during a period of eight minutes: and immediately quenching said reheated steel. substantially as described.

6. The process of treating steel which consists in subjecting the same to a bath of molten metal having a temperature of substantially 1400 F. and imparting to said steel within a period of less than ten minutes more than 125 British thermal units of heat for each pound of steel: immediately quenching the heated steel in a bath containing salammoniac. alum. and common salt; .maintaining said bath between predetermined limits of temperature; reheating said steel to a temperature of substantially 1000 F.. and imparting thereto less than 125 British thermal units of heat for each pound of steel during a period of eight minutes; and immediately quenching said reheated steel, substantially as described.

7. The process of treating steel which consists in immersing the same in a bath for a predetermined time while maintaining said bath at substantially the critical temperature of the steel thereby imparting to said steel. in less than ten minutes more than 125 British thermal units per minute for each pound of steel: quenching said steel in a bath maintained at a substantially constant temperature thereby taking from said steel a predetermined number of thermal units: reheating said steel to substantially 1000 F. thereby imparting to said steel in less than ten minutes more than 125 British thermal units per minute for each pound of steel: and cooling said reheated steel in a bath maintained at a substantially constant temperature. substantially as described.

In testimony whereof I afiix my signature, in presence of two witnesses.

CHARLES HENRY AUGUSTUS FREDERICK LOCKHART ROSS. W'itnesses:

T. A. WrrHERsrooN, FRANK C. TITUs.

immediately 

